Mg(SO 3 CF 3 ) 2 (Mg(OTf) 2 ) is a simple and cost-effective magnesium salt, which can promote the future applications of rechargeable magnesium batteries (RMBs). However, the simple Mg(OTf) 2 /ether electrolytes suffer from poor electrochemical properties due to the low solubility of Mg(OTf) 2 and the serious decomposition passivation of the [Mg 2+ -OTf − ] ion pair on Mg. Herein, the OTf − anion is successfully grafted on low-cost fluoride boronic esters (B(OC x H y F 2x-y+1 ) 3 ) to obtain the asymmetric and weak-coordination boron-center [B(OC x H y F 2x-y+1 ) 3 OTf] − anion in ether electrolytes. The -OCH 2 CF 3 (TFE) groups in B(TFE) 3 effectively realize the charge delocalization of the OTf − and B-O plane, restraining the independent decomposition of the [Mg 2+ -OTf − ] ion pair. The co-decomposition of the asymmetric [B(TFE) 3 OTf] − induces the formation of the B-containing organic/inorganic interphase, thus achieving a reversible Mg plating/stripping. After the further solubilization reaction, the obtained electrolyte exhibits a high average coulombic efficiency of 98.13% and long-term cycling stability (1000 h). Notably, the long cycling life (capacity retention of 90.2% after 600 cycles at 1 C) and high-rate capacity (43.0 mAh g −1 at 5 C) of the Mg/Mo 6 S 8 full cell demonstrate a favorable electrolyte/cathode compatibility. This work brings new insights to design the new-type and low-cost Mg-salts and high-performance electrolytes for commercial RMBs.
Liu Yan,Qian Li,Li Xiaogang,Tian Yuqing,Ma Jiaping,Song Siyu,Zhang Yixian,Yuan Aihua,Tian Huajun
Rechargeable magnesium
batteries are promising next-generation
energy storage systems owing to the low cost and high natural abundance
of magnesium. However, their practical application is critically impeded
by the parasitic decomposition of conventional electrolytes at the
Mg anode, leading to the formation of a passivation layer, high desolvation
barriers, and poor cycling stability. Herein, triethyl phosphate (TEP)
is introduced as a cosolvent into the Mg(OTf) 2 + MgCl 2 -DME electrolyte to regulate solvation structures and interfacial
chemistry. Comprehensive spectroscopic and electrochemical analyses
reveal that TEP facilitates salt dissociation and reconstructs the
Mg 2+ solvation structure, thereby reducing the desolvation
barrier and promoting ion transport. Meanwhile, TEP contributes to
the formation of a stable and robust solid electrolyte interphase
on the Mg anode, effectively suppressing side reactions and enabling
uniform Mg deposition. The Mg||Mg symmetric cell exhibits stable cycling
for over 3500 h with an overpotential below 0.2 V at 0.1 mA cm –2 and 0.05 mAh cm –2 . The Mg||Mo asymmetric cell delivers a Coulombic efficiency of 99.4%
after 3000 h at 0.5 mA cm –2 and 0.25 mAh cm –2 . Furthermore, the Mg||α-MnO 2 full
cell maintains a discharge capacity of 176.9 mAh g –1 after 350 cycles at 0.1 C. This work provides a solvation-regulation
strategy for designing high-performance Mg electrolytes.
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